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    <title>Document</title>
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<script>
    //异步
    setTimeout(function(){console.log('IIIII')},2000);
    console.log('I am Main');
    function YiBu(callback){
        setTimeout(function(){console.log(111);},3000);
        if(callback)
        {
            callback();
        }
    }
    YiBu(function(){alert('成功')});
</script>

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